Crude oil typically contains one or more solids such as asphaltenes, waxes including parrafins, hydrates and scale, among others. Further, in oil production, generally at some point oil such as crude oil is transported in liquid form through long stretches of pipes. The deposition of these solids from the crude oil onto the interior surfaces of the pipes can have a drastic and negative impact on the oil flow through these pipes.
Asphaltenes, in particular, make up one of the most polar fractions of crude oil, and often will precipitate upon an external stress such as temperature, pressure and/or compositional changes in the oil (resulting from blending or physical/chemical processing). Asphaltenes often precipitate, along with other solids such as paraffin waxes, when crude oil is transported via pipe, such as from a geologic structure to a wellhead via a production pipeline or from a wellhead or a storage vessel to a refinery via a pipeline. Asphaltene deposits can plug downhole tubulars, well-bores, choke off pipes and interfere with the functioning of separator equipment. Precipitated asphaltenes are not desirable, as they can foul and lead to fouling of process equipment.
Under many conditions, the solids present in a fluid will remain dissolved in the fluid. However, when deposition in a pipe occurs, it is generally undesirable because deposited solids can at least partially block the pipe and lead to reduction in the flow rate of the fluid in the pipe and require expensive and time-consuming cleaning of the pipe to restore the maximum or minimum acceptable flow rate of the fluid.
Asphaltenes are generally polyaromatic compounds and variably substituted with alkyl groups, along with heteroatoms such as oxygen, nitrogen, and sulfur and metal atoms (such as Ni, V, or Fe).
Asphaltenes are usually found in heavy crude oils and refinery normally in high quantities, and remain suspended in solution due to their small size and the possible solvating effects of other types of molecules in the petroleum oil or stream. These structures of several molecules are sometimes referred to as asphaltene particles. The asphaltene particles are generally smaller than twenty nanometers in size, but this can vary depending upon several factors such as their concentration in the oil.
It is known that insoluble asphaltenes may precipitate when two or more unprocessed petroleum crude oils and/or refinery process streams are blended together, such that the insoluble asphaltenes form asphaltene aggregates, or large precipitated clusters of asphaltene particles and molecules that stick together due to an attractive interaction. It is believed that this is reinforced when the nonpolar petroleum oil and/or refinery process stream is blended into the oil containing the asphaltenes. These aggregates can sometimes be observed with the unaided naked eye, and are typically physically and optically more dense than the surrounding oil mixture from which they precipitated. These aggregates tend to slowly sediment.